As an electron beam spin detector for use in a spin polarized scanning electron microscope (spin SEM) and a spin-resolved X-ray photoelectron spectroscope, there has been known a Mott detector which is lower in sensitivity than an electron detector by about four digits. For that reason, with an aim to improve the efficiency, a research has been pursued to devise a structure of the Mott detector in various laboratories (for example, S. Qiao, A. Kimura, A. Harasawa, M. Sawada, J. G. Chung, and A. Kakizaki, Rev. Sci. Instrum. 68, 4390 (1997)). However, under the existing circumstances, the efficiency is improved by about several times at the utmost, and a dramatic improvement would not be desirable in the future. As a spin detector of an entirely different type, there has been proposed a detector using a phenomenon in which a ferromagnetic body is irradiated with a spin-resolved electron beam, and a current absorbed by the ferromagnetic body at that time depends on the spin polarization degree of an incident electronic beam (for example, Th. Dodt, D. Tillmann, R. Rochow and E. Kisker, Europhys. Lett. 6, 375 (1988)). The principle of this detector derives from a fact that ease to enter an electron band structure of the ferromagnetic body is different depending on a direction of the electron spin. However, the sensitivity in this situation is slight higher in level than the Mott detector and lower than the normal electron detector by about three digits (for example, T. Furukawa and K. Koike, Jpn. J. Appl. Phys. 32, 1851 (1993)) .
On the other hand, in recent years, the development of magnetoresistive sensors each having a multilayer structure which are expected to the application to a read head of a hard disc and an MRAM has been advanced. Those magnetoresistive sensors are devices that can detect the above-described difference of current caused by the direction of spin with high precision, and the use of those devices leads to a possibility that there can be developed a spin detector with dramatic high sensitivity which is the same level as that of the normal electron detector. In fact, experiments that suggest the above possibility have been conducted (for example, H.-J. Drouhin, J. Appl. Phys. 97, 063702 (2005)). Also, in contrast to the Mott detector that must accelerate an electron beam to be measured up to a level of 100 kV, an incoming voltage to the magnetoresistive sensor is desirably equal to or lower than 1 kV. For that reason, there is a possibility that the entire spin detector that is small in size and low in costs can be manufactured.